1. Field of Invention
This invention pertains to the art of methods and apparatuses used to determine a velocity flow profile at a boundary layer and more particularly to the use of a thermocouple rake to relate temperature differentials to a velocity flow profile.
2. Description of the Related Art
The flow profile near a surface is essential information needed to calculate viscous shear force, and to develop a turbulence model for computation fluid dynamic (CFD) application.
There are two general methods used in the art to measure the boundary layer velocity profile. One is a total pressure rake consisting of an array of total pressure probes on the order of 0.02 inches in diameter. The total pressure rake can produce very steady and reliable data, but the physical requirements of the device prevents measurements extremely close to the surface.
Another method uses what is termed xe2x80x9chot-filmxe2x80x9d or xe2x80x9chot-wirexe2x80x9d as set forth in U.S. Pat. No. 4,727,751. These type of devices have the disadvantages of higher uncertainty in the measurements and greater susceptibility to breakage. Also, thermal transfer concerns create an inability to obtain measurements close to the surface. Such thermal transfer concerns are not encountered in the use of the present invention.
U.S. Pat. No. 4,587,843 is directed to a thermocouple-type gas-flow measuring apparatus including a plurality of thermocouples formed in series on a substrate. The series of thermocouples is used to enhance the signal amplitude to provide the stream velocity of a fluid, rather than a velocity profile provided by the present invention.
None of the above mentioned devices or methods provide a velocity flow profile as close to a surface as can be produced by the present invention.
The present invention is directed to a fluid-flow measuring device which utilizes one or more pairs of thermocouples to provide a velocity flow profile.
In accordance with the present invention, there is provided an apparatus adapted for providing a velocity flow profile of a gas flowing over an associated surface wherein the gas is associated with an initial flow direction. The apparatus includes a strut adapted to stand vertically from the associated surface, the strut including a constant thickness portion located between first and second ends, the constant thickness portion including a measuring surface being disposed parallel to the initial flow direction, a heater carried on the measuring surface for heating the gas as it passes the measuring surface, detecting means being operable to detect temperature differences from one side of the heater to the other side as the gas passes the measuring surface at successive predetermined heights above a reference line adapted to be aligned in parallel relationship to the associated surface and means for relating the temperature differences to gas velocity data at each of the successive heights whereby the gas velocity data at the successive heights provides the gas velocity profile.
According to another aspect of the invention, the detecting means includes a plurality of thermojunction pairs carried on the measuring surface, wherein one of each of the thermojunction pairs is located on a first side of the heater and the other one of the thermojunction pair is located on a second side of the heater, and wherein successive pairs of thermojunctions are located at the successive predetermined heights.
According to another aspect of the invention, the apparatus includes a first electrically conductive material carried on the measuring surface and extending between the first and second sides of the heater and being electrically insulated therefrom, and a second electrically conductive material carried on the measuring surface, the second electrically conductive material joining the first electrically conductive material on the first side of the heater to form the thermojunctions on the first side of the heater and joining the first electrically conductive material on the second side of the heater to form the thermojunctions on the second side of the heater.
According to another aspect of the invention, the first electrically conductive material is selected from the list consisting of chromel, alumel, platinum, platinum alloys, gold, and the like.
According to another aspect of the invention, the second electrically conductive material is selected from the list consisting of chromel, alumel, platinum, platinum alloys, gold, and the like.
According to another aspect of the invention, the heater comprises a material selected from the list consisting of alumel, platinum, and the like.
According to another aspect of the invention, the strut is formed of quartz, or any other low heat conductive material.
According to another aspect of the invention, the first and second ends of the strut are beveled.
According to another aspect of the invention, there is provided a method for providing a velocity flow profile of a gas flowing over an associated surface. The method includes the steps of providing a device having a measuring surface adapted to be aligned perpendicularly to the associated surface, the device being operable to determine gas velocity at successive predetermined heights above a reference line as the gas flows past the measuring surface; causing gas to flow past the measuring surface; obtaining gas velocity data at the successive predetermined heights; and, utilizing the gas velocity data to provide a velocity flow profile.
One advantage of the present invention is that a velocity flow profile can be attained very close to the reference surface.
Another advantage of the present invention is that the gas velocity data may be obtained simultaneously at various heights to provide a simultaneous velocity flow profile.
Another advantage of the present invention is that flow reversals can be detected and measured.
Another advantage of the present invention is that the turbulence levels at various heights can be obtained simultaneously close to the reference surface.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.